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Re: R: R: About hardfloat in ppc

From: Yonggang Luo
Subject: Re: R: R: About hardfloat in ppc
Date: Thu, 30 Apr 2020 15:26:11 +0800

On Thu, Apr 30, 2020 at 10:18 AM Richard Henderson <address@hidden> wrote:
On 4/29/20 5:20 PM, 罗勇刚(Yonggang Luo) wrote:
> Question, in hard-float, if we don't want to read the fp register.
> for example: If we wanna compute c = a + b in fp32
> if c = a + b In hard float
> and if b1 = c - a in hard float
> if b1 != b at bitwise level, the we se the inexat to 1, otherwsie 
> we set inexat bit to 0? are this valid?
> we can also do it for a * b, a - b, a / b. 

That does seem plausible, for all of the normal values for which we would apply
the hard-float optimization anyway.  But we already check for the exceptional

    if (unlikely(f32_is_inf(ur))) {
        s->float_exception_flags |= float_flag_overflow;
    } else if (unlikely(fabsf(ur.h) <= FLT_MIN)) {
        if (post == NULL || post(ua, ub)) {
            goto soft;

I means remove of all thse  exceptional cases, and detecting float exception by hard float operation.  



Yonggang Luo

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